Visual speech perception involves
perceiving language from faces. This fact
is interesting because the language and face perception functions are usually
considered to be very separate. How much of visual speech perception involves
the language function and how much involves the face function?

Many scientists have thought
that visual speech has little to do with face perception. After all, we look
at different parts of the face for visual speech perception (mostly the mouth)
and face recognition (eyes, nose, mouth, configuration of these features,
and face shape). There is also evidence that we use different parts of our
brains for visual speech perception and face recognition. However, some new
findings suggest that the face function might be involved with visual speech
perception in an interesting way. . .

The Margaret Thatcher Effect:The
demonstration above is called the "Margaret Thatcher Effect" (named
after the former Prime Minister of England whose face is depicted). Look at
the face on the left. The eyes and mouth of Margaret Thatcher have been inverted
relative to the rest of her face. It's interesting that these distortions
are much easier to notice when the face is upright than when it is
upside-down.

What the effect means:
The Margaret Thatcher Effect demonstrates that seeing an upright face makes
it easier to notice distortions in the face image. The effect adds to other
findings that show we are especially sensitive to the information contained
in upright faces. In fact, it is much easier to recognize an upright face
than an inverted face. Furthermore, many scientists believe that this heightened
sensitivity to the upright image is specific to face perception. But
what about visual speech perception? Please read on. . .

The 'McThatcher Effect':The demonstration below tests visual speech
perception by combining the McGurk Effect and Margaret Thatcher Effect (hence,
the 'McThatcher Effect'). In the video below, you will see five audiovisual
syllables produced by these face (and lip) images:

The video shows these images
in order from left to right. Watch the mouth closely, but concentrate on what
you're hearing. The movie will repeat itself until it is stopped. You can
watch it as many times as you need to be sure of the syllables you hear. After
you feel certain of what you perceive, stop the movie and continue reading
the text below.
PLEASE START THE MOVIE NOW.

If you're like most people,
what you hear depends on which face (or lip) image you see. Here is what most
people report:

'Va'

'Va'

'Va'

'Ba'

'Va'

If you would like, you can now
play the movie over and see if you perceive VA from all of the images except
for the fourth.

How the stimuli were made: All
five of these stimuli were made by dubbing an auditory BA syllable onto a
visual syllable VA According to the McGurk effect, most people report perceiving
VA with this syllable combination. However, these images were also manipulate
in other ways. As you can see, some of the images show an inverted face. If
you look closely, you may also notice that in some images, the mouth is inverted
relative to the face. Finally, the last image is of an inverted mouth without
a face. These manipulations were accomplished by using a computer to digitally
isolate and invert the mouth and face. To see a picture
of the equipment used to create these stimuli,CLICK
HERE.

What the effect means: For
most people, all but the fourth image produces a McGurk effect. What is special
about the fourth image? This image is composed of an upright face with an
inverted mouth. It is much like the Margaret Thatcher effect image. As discussed
above, the Margaret Thatcher effect demonstrates that seeing an upright face
increases our sensitivity to image distortions. Similarly, the visual speech
'McThatcher effect' shows that an upright face increases our sensitivity to
articulatory distortions. Specifically, the upright face enhances our
sensitivity to the upside-down mouth so that it can no longer induce the McGurk
effect. Notice that the upside-down mouth can still produce the McGurk effect
when it is shown in the context of an inverted face (Image #2), or when it
is shown without any face context at all (Image #5). The McGurk effect disappears
only when the inverted mouth is shown in the upright face.

So, upright
face information seems to be important for both face perception and
visual speech perception. It heightens
sensitivity for both functions. This could mean that the two functions are
more closely related than was originally thought.